MONROVIA, Aug 18 (Reuters) - Investments in mining, agriculture and oil will push Liberia's economic growth into double-digits within five years, but it will still need U.N. peacekeepers to help keep order until 2017, the president said.

Speaking on the 10th anniversary of the end of 14 years of on-off civil war, President Ellen Johnson Sirleaf told Reuters peace, investment and an eightfold-fold increase in government revenues were concrete signs of recovery.

But corruption remained a problem, and the huge numbers of unskilled young people - many of them still traumatised by the conflicts - would threaten stability until they got more opportunities, she said.

Two wars between 1989 and 2003 killed about 250,000 people and led to a complete collapse of the state. It was carved up by warlords who often used child soldiers and fought over control of diamond and timber concessions.

The West African country - stabilised by a U.N. peacekeeping mission and under of the leadership of Nobel Peace Prize winner Sirleaf since 2006 - is slowly recovering and has since lured major investors.

"There is no quick fix in recovery ... We have not reached where we want to (be) but the results are underway," Sirleaf said on Saturday in her office.

The former World Bank official said annual government revenues were now around $600 million, up from $80 million when she came to power. There had been more than $16 billion in foreign investment under her tenure and the 7.2 percent growth forecast for 2013 was conservative, she added.

"We can do much better than 7 percent. We are heading for double digits," she said. Existing mining projects, which account for 60 percent of revenues, would be boosted by agriculture and the potential of the oil sector.

Double digits would be a significant jump from recent years, when expansion was between 6.1 and 8.3 percent, according to the IMF. The Fund and Liberia's central bank have not released forecasts as far ahead as 2018, the year Sirleaf expects growth to hit her target.

"Agriculture is going to take over in the near future. Whether it is oil palm or rice, it will pass mining. Give it three or four years," Sirleaf said.

ArcelorMittal, the world's largest steelmaker, BHP and other firms have moved in to tap iron ore reserves.

Fertile land has attracted Golden Agri's Golden Veroleum and Sime Darby to invest in palm oil - used in everything from cooking to bio diesel.

Oil majors Chevron Petroleum and Exxon Mobil Corp have snapped up major stakes there, lured by the prospect of offshore reserves.

U.N. WON'T STAY FOREVER

Sirleaf has won praise abroad for her role in the recovery, but faced domestic critics, among them Leymah Gbowee, the rights activist with whom she shared the 2011 Nobel Prize for their work defending women's rights during the war.

Some activists say she has not acted quickly enough to root out corruption and nepotism. A report commissioned by the government showed nearly all resource deals since 2009 broke Liberia's own laws.

Sirleaf recognised problems but remained bullish.

"The war against corruption is being won but not at the pace we expect it. We have fired many people. We have won some cases in court. But capacity in some areas is still low."

There are currently just over 7,000 U.N. soldiers and policemen, half the number from the mission's peak. In a sign of further progress, Liberia has contributed peacekeepers to a U.N. force in Mali.

"At some point, Liberia will have to take its own responsibility ... (the United Nations) will not stay in any country forever," she said. "They will keep a small force here, perhaps up to the 2017 elections."

Huge numbers of unskilled young people still looking for work remained a problem.

"They are a vulnerable group that can be misused and misled," she warned. "They will remain a threat until we respond by giving them training, employment and by making them feel that they too have a full part in the society."

"I just hope they will continue to exercise patience." (Writing by David Lewis and Bate Felix; Editing by Andrew Heavens)

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